As with other types of internal combustion engines, two-stroke engines comprise a crankshaft disposed in a crankcase for converting the linear movement of the engine's piston, or pistons, into rotating torque. The crankshaft usually comprises a crankshaft body made of a single piece of hard material, such as steel, and the main components of the crankshaft are integrally formed with the crankshaft body. In some instances, the crankshaft body may also be made of parts connected together by various means known in the art. The crankshaft is rotatably connected to the crankcase via a plurality of main bearing assemblies, and rotatably connected to the connecting rods transmitting the energy generated by the pistons via connecting rod bearing assemblies. Since the crankshaft usually rotates at high speed within the crankcase, the various bearing assemblies connected thereto, including the connecting rod bearing assemblies, need to be appropriately lubricated.
Two-stroke engines do not generally have sophisticated pressurized lubrication systems for lubricating all the various components of the crankshaft and the various components connected thereto such as those generally found in four-stroke engines. This is particularly true regarding vertically oriented two-stroke engines used in marine outboard engines.
In particular, it is know in the art to lubricate the connecting rod bearing assemblies of vertically oriented two-stroke engines by spraying lubricant within the crankcase in the vicinity of the connecting rod bearing assemblies rotating path using low capacity lubricant pumps. U.S. Pat. No. 5,193,500 and U.S. Pat. No. 5,375,573 provide examples of such connecting rod bearing assemblies lubrication systems.
However, since lubricant is not discharged directly within or close to the connecting rod bearing assemblies, a significant volume of lubricant is required to appropriately lubricate the connecting rod bearing assemblies. Furthermore, a significant portion of the lubricant sprayed into the crankcase finds its way to the combustion chamber of the cylinders, and incomplete combustion of such lubricant within the combustion chamber increases the engine's pollutant emissions.
In view of the above, there is a need for a vertically oriented two-stroke engine having a lubrication system for the connecting rod bearings assemblies discharging a limited volume of lubricant in the vicinity of such connecting rod bearing assemblies so that less lubricant need to be used and less lubricant is ultimately burned in the combustion chamber, which entails that less pollutant emissions are release in the atmosphere when the two-stroke engine is used.